rust-based-os-comp2022/guide-code/ch1-3mini-rt-usrland/src/main.rs

// os/src/main.rs
#![no_std]
#![no_main]
#![feature(panic_info_message)]

mod lang_item;
#[macro_use]
mod console;

const SYSCALL_EXIT: usize = 93;
const SYSCALL_WRITE: usize = 64;

fn syscall(id: usize, args: [usize; 3]) -> isize {
    let mut ret;
    unsafe {
        core::arch::asm!(
            "ecall",
            inlateout("x10") args[0] => ret,
            in("x11") args[1],
            in("x12") args[2],
            in("x17") id,
        );
    }
    ret
}

pub fn sys_exit(xstate: i32) -> isize {
    syscall(SYSCALL_EXIT, [xstate as usize, 0, 0])
}

pub fn sys_write(fd: usize, buffer: &[u8]) -> isize {
    syscall(SYSCALL_WRITE, [fd, buffer.as_ptr() as usize, buffer.len()])
}

#[no_mangle]
extern "C" fn _start() {
    print!("Hello ");
    println!("world!");
    sys_exit(9);
}